1. Field of the Invention
The present invention relates generally to plug valves of the type having an inlet and an outlet and a valve body in which a plug with a waterway therethrough may be configured to provide a path from the inlet to the outlet through the waterway for passage of a fluid therethrough or may alternatively be positioned with the waterway perpendicular to the inlet and outlet for blocking the flow of fluid therethrough. The present invention relates more specifically to a retracting seal valve in which two distinct pairs of slips are slidably attached on respective oppositely tapered surfaces of the plug wherein vertical upward motion of a tapered faceted cylindrical plug causes seal retraction of one pair to permit a quarter turning motion of the plug to open the valve and wherein in continued upward motion of the plug wedges the perpendicular pair outwardly, the reseating slip seals allowing the retracted slips to be changed without draining the line and without leakage from the waterway into the valve body.
2. Prior Art
Plug-type valves are well-known in the art. Often such plug-type valves are implemented with slips and seals in a seat and reseat configuration. The slips and seals provide means for blocking the flow through the valve at both the inlet and outlet ports when the valve is in the closed position. This permits maintenance personnel to bleed the valve body with the valve in its closed position with a minimum expenditure of time and labor costs. Typically, the plug slips are interconnected so that in opening the valve from its fully closed position, (beginning with the valve in the seated/closed position) the first motion of the plug is upward vertical in one direction which has the effect of retracting the slips from the inside surface of the valve body in order to prevent scoring of the valve seals in the subsequent motion when the valve is turned to place the flow passage to be in line with the inlet and outlet. However, in conventional plug-type valves which employ slips and seals as described above, after the flow passage has been partially aligned with the inlet and outlet, vertical motion of the plug is then again required in a direction opposite to that of the initial vertical motion (downward) which retracted the slips. This second oppositely directed vertical motion in effect reseats the valve by placing the flow passage in the plug in intimate contact with the inlet and outlet respectively and finishing alignment. This motion drags a tapered plug across a tapered body.
Although such seat and reseat valves have had good commercial success, the aforementioned motion of the plug in opening or closing the valve, namely, vertical motion in a first direction, the 90 degrees rotation and then vertical motion in a second direction opposite to the first, generally increases the cost of the valve because of the complexity of the operator mechanism to which the plug is connected. The operator mechanism is complex because it has a three piece stem set to transform the aforementioned vertical motion, rotational motion and oppositely directed vertical motion into a undirectional motion in a hand operator or automatic operator. Consequently, the cost of manufacture, maintenance and repair of such a complex operator is higher than it would be if it were possible to simplify the motion of the plug between the valves open and closed positions. For example, if it were possible to design a plug-type valve in which the motion of the plug were vertical, rotational and vertical in opening and closing, wherein both vertical portions of the operation sequence were in the same direction for opening the valve and in the same direction for closing the valve, then the operating mechanism to which the plug trunnion were attached would be significantly simpler. The operator would also be less costly to manufacture, maintain and repair thereby reducing the overall costs for the valve while still providing a double block and bleed feature of the prior art valves described above as well as the reseat feature which allows the slips to be changed without draining the line.
There are two basic types of retracting seal valves presently in existence. One such type is the twin seal valve. This type uses a vertical upward motion of a tapered faceted cylindrical plug to cause seal retraction followed by a quarter turning motion to open the valve. In this type of valve, clearance between the waterway and the body cavity prevails during the entire open status of the valve. As a result, the pipe line that is the source of fluid pressure to the valve must be drained to change slips. A second type of valve, normally referred to as a seat and reseat type, utilizes a vertical upward motion of a tapered faceted conical plug to cause seal retraction, followed by a quarter turning motion to open the valve. But the the seat and reseat type valve vertically descends a tapered conical plug to reseat, creating a metal-to-metal contact. In this type of seal valve, there is a minimal opening between the waterway and the body cavity which allows the slips to be changed without draining the line. However, the metal-to-metal reseat still permits some leakage. A third type of seal valve has been disclosed in U.S. Pat. No. 4,623,119. This type of seal valve begins and ends with vertical upward motion using a tapered plug that is inverted compared to conventional plugs. This unidirectional motion solves the operator complexity problem in this type of seal valve, the opening between the waterway and the body cavity is minimal, thus allowing the slips to be changed without draining the line. But once again, some leakage is expected between the waterway and the body cavity when the valve is opened.
Thus based on the foregoing, it can be seen that all of the prior art seat and reseat type plug valves suffer the disadvantage of having at least a limited degree of leakage of the fluid between the waterway and the interior cavity of the valve body. Although such leakage is insufficient to require drainage of the line for replacement of maintenance of the slips, it is still inefficient and inconvenient in that some leakage of the line occurs during slip maintenance.
A preferred plug assembly and valve body cavity are cylindrical rather than conical. Cylindrical shapes are easier to machine and match. Also, wear due to direct contact between the plug and body cavity (i.e., rubbing) is easier to avoid in a cylindrical plug/cavity seat and reseat plug valve. Furthermore, cylindrical bodies can be standardized to increase productivity.
Thus, there is a continuing need for a seat and reseat plug type valve in which there is both a unidirectional opening or closing action as well as no leakage between the waterway and the interior cavity of the valve body when the valve is in its open position, thus making it possible to simplify the valve operator body and plug and to replace and maintain seals without draining the line, but also to incur absolutely no leakage during such slip maintenance.